Lighting fixture having a reflector with a compound curvature



June 19, 1951 E. B. KIRK 2,557,787

LIGHTING FIXTURE HAVING A REFLECTOR WITH A COMPOUND CURVATURE Filed Dec.18, 1947 2 Sheets-Sheet 1 IN VEN TOR. ED WARD B KIRH ATTORNEY June 19,1951 Filed Dec. 18, 1947 E. B. KIRK 2,557,787 LIGHTING FIXTUREHAVING AREFLECTOR WITH A COMPOUND CURVATURE 2 Sheets-Sheet 2 INVENTOR. EDWARDBKIRK ATTORN E Y Patented June 19, 1951 UNITED LIGHTING FIXTURE HAVING AREFLECTOR- WITH A COMPOUND CURVATURE Edward B. Kirk, New York, N. Y.,assignor to Donald Deskey Associates, New York, N. Y., a partnershipcomposed of Ralph G. Gulley and Donald Deskey Application December 18,1947, Serial No. 792,468

2 Claims.

This invention relates to a lighting fixture adapted to afford improvedlighting, especially lighting of areas which are unequal in twodimensions, such as halls and the like.

In the lighting of halls it has been the practice either to locate lightfixtures of relatively low intensity so close to one another that thesubstantially circular spots of light produced by each fixture willslightly overlap, or else, if higher intensity sources are used, toarrange light shielding means to prevent the light cast laterally fromrising higher on the walls than desired.

In the first case, maximum efiiciency can evidently be obtained only bylimiting the area cov-- ered by each fixture to a space which will beequal in both dimensions. This means that the fixtures must be spacedfrom one another by distances not exceeding the width of the hall. Whilethis procedure may be satisfactory for halls of relatively short length,it is not satisfactory for halls, the length of which is many times thewidth thereof, such as lengthy corridors and the like. In such cases,there is demanded theprovision of a great number of fixtures, each oflow intensity. Since the cost of a fixture is by no means proportionateto the luminous intensity of the output thereof, it follows that anarrangement which would allow the employment of a lesser number offixtures of higher intensity would be less costly. Additionally, theefficiency of modern light sources is very much greater for units ofrelatively large size. In the case of the almost universally employedtungsten electric lamps, the output in lumens for each unit ofelectricity consumed is almost doubled, in passing from the watt bulbadapted to satisfactorily illumine a narrow hall, to a bulb of 200watts. Therefore a lighting system employing fewer high intensity unitswould not only be less costly to install, but would be cheaper in powerconsumption.

If the second alternative method of employing fixtures which yield acoverage greater than the width of the hall be employed, then there willbe an unnecessary amount of light emitted in the cross dimension of thehall. While this may be cut off by shades, so that it does not rise togive undesired illumination of the walls of the hall, yet this willresult in a loss of efficiency which may more than offset the highereificiency of the luminous sources.

The ideal light fixture for duty of the type described, would be afixture in which the normally circular pattern of light distributionwould be altered into a pattern of a form wherein the major and theminor axes bear to one another a ratio several times unity. In thisfashion lateral coverage of the hall would be only that needed to reach2 the walls, while longitudinal coverage would allow the use of fewerfixtures, much more widely spaced from one another. 4

One object of the present invention is to provide a light fixture whichshall produce, with high efficiency, a light pattern of the type lastdescribed.

Another object of this invention is to provide a fixture wherein thelight primarily emitted from a relatively high power source is actedupon by optical reflective devices so that the pattern cast in twoperpendicular dimensions is deformed from a circular shape to a shapeapproximating an ellipse, which shape is conveniently termed elliptical.

A further object of this invention is to provide a fixture of the typedescribed, in which the reflection of the light is accomplished in suchfashion that light is not merely screened from areas which it is notdesired to illuminate, but is actually changed as to path, so that itreinforces the light in a longitudinal direction, thereby affording muchhigher optical efiiciency of the fixture as a whole.

A still further object of this invention is to provide a fixture inwhich two distinct optical reflective systems are provided, each actingat right angles to the other, the one designed to give a narrow beam,and the other to yield a widespread beam, but substantially in onedimension only, the over-all light distribution then approaching thetheoretically desired elongated rectangular form, by suitable andrelatively slight overlapping of beams from adjacent fixtures.

An additional object of the present invention is to provide a lightingfixture adapted to efficiently and adequately illuminate relativelynarrow and lengthy corridors, and the like, of which fixtur the luminousoutput shall be emitted without substantial wasteful absorption, and yetshall be of a generally elliptical character with respect to the patterncast upon a plane surface forming the floor of the corridor.

Yet another object of this invention is to provide a fixture having theadvantages already enumerated, and additionally avoiding the incidenceof direct rays from a light source possessing high intrinsic brilliancy,upon the eyes of persons passing along the hall illuminated by aplurality of such fixtures. v

Still another purpose of this invention is to provide a lighting fixturefor narrow passageways, which shall emit light in a pattern adapted tocover a relatively great length of the passageway, and yet shall emitonly sufficient light to cover the width thereof.

Other objects and advantages of the present invention will be apparentto those skilled in the lighting art from the following description, andfrom the .drawings. hereunto annexed.

The drawings represent, by way of example and not of limitation, oneembodiment of this invention.

Figure 1 is a hyperbolic curve showing the general form of thelongitudinal reflector of this fixture.

Figure 2 is an elliptical curve showing the general form of the lateralreflector of this fixture.

Figure 3 is a side elevation of the fixture.

Figure 4 is an end elevation of the fixture.

Figure 5 shows a lateral cross-section of an alternative form offixture.

Figure 6 shows a cross-section of the lamp proper and the supportinglight shield covering the same.

Referring to Figure 1, reference numerals 5 and '6 are foci of conjugatehyperbolas, upon the transverse axis 1, only one'hyperbola 8 beingshown. This is'constructed according to the well known equation:

the ratio of -a to b being determined by the desiredlongitudinal spreadof the light.

Referring now additionally to Figures 3 and 6 it will be seen that in'the longitudinal direction the-reflector 9'-is shaped in the form of a'generally hyperbolic curve, as just discussed. This reflector issupportedat the central point thereof 'by-a-hollow metal tube I0,aflixed to the ceiling by a'flange' II and carrying therewithin theconductors (not shown) for supplying electrical en- 'ergytothe bulb orlampiproper. The bulb I2 is coated over the lower or neck portionthereof 'with an-opaque reflective coating I3. The use of'such-areflective coating, usually formed of a metalpossessing highreflectivity, is well known in the art. Such coating may be appliedeither to the-interior or to the exterior surfaces of the -'bulb,andserves both to prevent direct passage of light downwardlytherefromand to increase the luminous flux-in-anupward direction. Alternatively,aseparate reflector independent of, and exterior to the bulb, maybeemployed for the same purpose.

The bulb-I2 is supported by'a socket I4, which is *mechanically andelectrically adapted to receive the base of the bulb. Socket I 4 issupported bya-hollow metallic tube I5 which is bent upwardly at anoutwardly flaring angle, until it reaches the point I 6, where itcontinues inwardly and terminates in a suitable supporting body *I'I.aflixed-to tube In. The electrical conductors pass through flange II,tube In and tube I5, in order to reach the socket I4. From supportingbody IIranothertube :I8 is downwardly and outwardly flared as far aspoint I9, when it bends inwardly and terminates at'20. An outer lightshield'ZI is aflixed to-the end 20 of tube I8 by means of screws 22. Allmetal portions above the ,top of the shield are preferably made withflat black surface finish on the exterior thereof, in order to prevent.unwantedreflection therefrom of any stray light incident thereupon. Anair vent .23 allows cooling of the bulb.

It is to be understood that the mechanical details just given arepurelyillustrative, and that other forms of supporting and shielding devicesmay be substituted for those here shown, provided that the opticalfunctioning thereof is substantially identical.

.desirable.

Reference is now made to Figure 2, illustrating a portion of an ellipse.Foci 30 and 3I, on major axis 32, with minor axis 33, determine thecurve 34, as well known in geometry. The lateral reflector of thisfixture is slightly modified from a true ellipse of this character byhaving the minor axis increased, while keeping the major axis and focias shown in Figure 2. The exact amount of this alteration can not beprecisely stated, as it'is dependent upon a number of considerations.Since the light source is never a true geometrical point,.the,well knownreflective properties of an elliptical reflector, giving rays whichcross one another, -fail to be perfect and precise. The larger theeffective source of light, the greater the deviation from a trueellipse, is found to be Therefore the theoretical equation:

bulb is employed, it has been found that the frosted glass acts asequivalent to a roughly "sphericaleobject'emitting about of the' light,

so that in this case the ellipse may be considerably modified in themanner above described. As larger lamps are used, still furthermodification must be made to maintain high efficiency.

Yet another reason for modifying the true elliptical shape is'to allowthe hyperbolic and elliptical reflectors to be blended together, wherethey intersect above the lamp bulb. It has also been found highlydesirable, in order'that maximum efliciency and correct optical patternsbe obtained, to finish the optically active surfaces of both portions ofthe reflector to a specular, and not a diffusing finish.

Considering now the manner in which light is distributed by this hybridreflector, it is first to be noted that the bulb shielding structureacts as a light barrier below the reflective system, and since nolightis cast directly downward, except such as proceeds from the reflector,the bulb shield tends to cause a spot, immediately beneath the fixture,of decreased illumination, which would be highly undesirable.

In order better to understand how the difliculty just described isovercome in the present invention, consideration may be given to themanner in which-each portion of the reflector functions. The hyperbolicportion of the reflectoracts, as well known 'in optics, so that any rayproceeding from one focus is reflected in a fashion as though itproceeded linearly'from theconjugate focus. Thus a widely divergent beamin the longitudinal direction of the fixture is obtained.

-IIoweverthis does notprevent the formation of aquasi-shadow regiondirectly beneath the bulb housing, in as far as the rays oflight'proceeding from'the hyperbolic reflector portion are concerned.

Attention is now called to the opticaloperation of the fixture in alateral direction. This is most conveniently done by considering thisportion of the reflector as though it'were a true ellipse, the-departurefrom this form previously mentioned not materially altering the actionnow tobe described. The rays reflected from the elliptical portion donotultimately spread to as great an extent as those coming from thehyperbolic portion, so that the fringe of the optical pattern in thelateral direction may be made to coincide with the wall-floor line ofthe passageway which it is desired to illumine, while the raysproceeding from other portions of the ellipse will cross one anotherbeneath the lamp housing, whereby the portion of the floor directlybeneath the fixture will receive, from the elliptical refiectiveportion, approximately twice the amount of light received by portions ofthe floor situated laterally from the fixture, and not directlytherebeneath. Since the portion thus doubly illuminatec is substantiallyidentical with that lying in the quasi-shadow region of light reflectedfrom the hyperbolic portion of the reflector, a compensatory efiect isobtained. In practice, due to penumbral effects, actual measurementsshow that it is possible, by the artifice just described, to obtain alight pattern which is substantially free from any perceptible undesiredshadow field. In like manner, shadow effects caused by portions of thebulb supporting elements are substantially eliminated. It is alsoevident that no direct rays from the bulb proper can strike the eye of aperson situated beneath the fixture.

Attention is now called to Figure 5, which is a schematic showing of analternative method of supporting the lamp bulb within the fixture. Inthis form the bulb 48 may be provided with a bowl portion il, throughwhich light reaches the inner reflective surface of ancillary reflectiveshield 42. However it is preferred to make the portion 4| of the bulbwith a completely opaque and reflective coating, so that element in mayfunction purely as a shield, keeping direct rays from a person beneaththe fixture. In this latter case, the shield may be formed in anysuitable decorative shape, if so desired. Element 43 is the ellipticalportion of the reflector, which latter is formed substantiallyidentically with the previously described form, having a lateralelliptical portion, and a longitudinal hyperbolic portion, the latterportion not being shown in this figure.

This form of construction allows the lamp bulb to be supported directlyin a socket All, afiixed to the ceiling by the element 45, of anyconvenient form. In this fashion the cost of construction may besomewhat reduced, owing to the much simpler bulb shield. However it hasbeen found, With this type of fixture, that it is extremely difficult toavoid the projection upon the eye of an observer of a brilliant anddisturbing spot of light, due at least in part to the brilliantlyillumihated uncoated neck portion of the bulb, which is not situatedclosely enough to the focal points of the reflector system to have lighttherefrom properly reflected.

From the foregoing description it will be evident that the fixture ofthe instant invention affords means for efficiently illuminatingelongated areas, with minimum loss of luminous flux, and for allowingthe placement of fixtures at considerable distance from one another, byproper orientation of the reflectors, so that the axis of the hyperbolicportions thereof lies along the axis of the hall or passageway in whicha plurality of fixtures are placed. Furthermore, this fixture providesmeans for illuminating hallways, whereby the luminous pattern emitted islaterally confined within desired limits, while at the same time thelongitudinal extent of the pattern is enhanced to a substantial degree.

A further advantage of the fixture of this in- Vention is that acompletely effective shielding of direct light rays is provided at allpoints illumined 6 by the fixture, and yet no blind spot exists in thefield of illumination.

Among the uses of the fixture of this invention are the illumination ofareas of all kinds which are of a length great in comparison with thewidth thereof. This includes display cases, show counters, highways,tunnels and the like. For street lighting the fixture may be tiltedslightly, in order to secure a better distribution pattern whgn notmounted over the middle of the street.

While there have been shown and described certain embodiments of thisinvention, it is to e understood that these are by way of illustrationonly, and that various alterations and extensions will become apparentto those skilled in the illuminating art. Therefore the scope of thisinvention is limited only by the hereunto appended claims.

Having now fully shown and described this invention, what is claimed anddesired to be secured by Letters Patent of the United States of Americais:

1. An illuminating ceiling fixture comprising in combination, means forsupporting a substantially spherical source of light, a shield situatedbelow and at least partly around .said light source, means forprojecting light upwardly from said source, and a hybrid reflectorlocated substantially horizontally above said source and receiving lighttherefrom, said reflector having a generally hyperbolic shape in onedimension and having a generally elliptical shape in a dimension atright angles to said first dimension, the relative position of saidlight source and said hybrid reflector being such that the floor belowsaid fixture is illuminated in a pattern extending in the direction ofthe conjugate axis of said hyperbola for a distance several times thedistance in which it extends in the direction of the minor axis of saidellipse, said light source being provided with opaque means forsubstantially preventing downward direct projection of light therefrom,and being provided with means of reflective character for re-projectingupwardly light proceeding from said source.

2. An illuminating fixture according to claim 1, in which saidelliptical portion of said reflector has the minor axis thereof of adifferent length relative to the major axis and the foci than for a trueellipse, whereby said light source may be a standard size frosted lampbulb, while yet maintaining good efiiciency of light distribution fromsaid fixture.

EDWARD B. KIRK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 744,692 Ryan Nov. 17, 1903999,813 Losey Aug. 8, 1911 1,758,041 Heyman May 13, 1930 1,898,167 BeanFeb. 21, 1933 2,014,012 Wood Sept. 10, 1935 FOREIGN PATENTS NumberCountry Date 720,138 France Dec. 3, 1931 OTHER REFERENCES PublicationData Sheet #13 Garden City Plating 00. January 18, 1935, 240-78 L. D. 5.

